I have two computer at home one mine (Admin) and the other belongs to my sister I need some software to take over her computer and support it. I also want to teach her to support by herself the computer so i need her to see what I'm doing.
what is the best\most suitable software for this?

Questions on Server Fault are expected to relate to server, networking, or related infrastructure administration within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here.
If this question can be reworded to fit the rules in the help center, please edit the question.

get a free logmein account its simply, free and works really well and best of all it doesnt require any firewall configuration so you should be able to talk your sister through the setup over the phone and then log in remotely etc

+1. I use this for friends and family and it works pretty well. Easy to use, free, nothing to configure, I can see what they're doing and vice versa. It saves me the road trip to Aunt Martha's house when she's having email trouble. ;)
–
joeqwertyOct 23 '09 at 11:23

If you are only doing it every now and then, check out Copilot. Not software installs and really easy to get setup. Takes about 4 clicks on even the most restrictive vista uac crappness and I've yet to come across anyone who couldn't get it setup.

UltraVNC SC does not require
installation and does not make use of
the registry. The customer only have
to download the little executable and
Click to make a connection. The
connection is initiated by the server,
to allow easy access thru customers
firewall.